Field of Invention
The present disclosure relates to an electronic apparatus and a control method, and, particularly, to an electronic apparatus and a control method that having an oscillating frequency that is not affected by the temperature.
Description of Related Art
The communication systems and microprocessors nowadays often use phase-locked loop circuits to provide stable high frequencies. As a result, phase-locked loop circuits are widely used in electronic products such as digital televisions and communication chips.
In general, phase-locked loop circuits include a coarse-tune circuit block and a fine-tune circuit block. At first, the coarse-tune circuit block controls a digital controlled capacitor array (DCCA) based on digital signals to vary a capacitance of a LC resonant cavity so as to select an appropriate frequency band firstly. After the frequency band is selected, varactors in the fine-tune circuit block is used to vary the capacitance of the LC resonant cavity to stabilize the loop and precisely output the target oscillating frequency.
However, the capacitance of the varactors in the fine-tune circuit block changes along with the temperature and affects the oscillating frequency outputted by the phase-locked loop circuits at the same time. As a result, when the variation of the oscillating frequency exceeds the variable range of the fine-tune circuit block, the phase-locked loop can not be stable and loses lock.
For such a phenomenon, additional varactors are often disposed in the phase-locked loop circuit such that the variation of the capacitance of these additional varactors affected by the temperature and the variation of the capacitance of the original varactors in the fine-tune circuit block affected by the temperature cancel each out. By using such a technique, the offset of the oscillating frequency due to the variation of the temperature is lowered. However, the additional varactors increase the capacitance of the system at the same time. The decrease of the variable range of the fine-tune circuit block is unavoidable. Further, the additional varactors also introduce new paths of noise and interference.